2 Vibration criteria
2.1 Types of vibration
Vibration in buildings can be caused by many different external sources, including industrial, construction and transportation activities. The vibration may be continuous (with magnitudes varying or remaining constant with time), impulsive (such as in shocks) or intermittent (with the magnitude of each event being either constant or varying with time). Examples of typical types of vibration and their sources are shown in Table 2.1.
Table 2.1 Examples of types of vibration
|Continuous vibration ||Impulsive vibration||Intermittent vibration|
Machinery, steady road traffic, continuous construction activity (such as tunnel boring machinery).
Infrequent: Activities that create up to 3 distinct vibration events in an assessment period, e.g. occasional dropping of heavy equipment, occasional loading and unloading.
Blasting is assessed using ANZECC (1990).
Trains, nearby intermittent construction activity, passing heavy vehicles, forging machines, impact pile driving, jack hammers.
Where the number of vibration events in an assessment period is three or fewer this would be assessed against impulsive vibration criteria.
Vibration in buildings may also occur from internal sources (within a building structure), such as a road development forming part of the building structure, or mechanical vibration sources in buildings.
Vibration and its associated effects are usually classified as continuous, impulsive or intermittent as follows:
- Continuous vibration continues uninterrupted for a defined period (usually throughout daytime and/or night-time). This type of vibration is assessed on the basis of weighted rms acceleration values presented in Table 2.2.
- Impulsive vibration is a rapid build up to a peak followed by a damped decay that may or may not involve several cycles of vibration (depending on frequency and damping). It can also consist of a sudden application of several cycles at approximately the same amplitude, providing that the duration is short, typically less than 2 seconds. Impulsive vibration (no more than three occurrences in an assessment period) is assessed on the basis of acceleration values presented in Table 2.2. Blast-induced vibration is assessed according to ANZECC (1990).
- Intermittent vibration can be defined as interrupted periods of continuous (e.g. a drill) or repeated periods of impulsive vibration (e.g. a pile driver), or continuous vibration that varies significantly in magnitude. It may originate from impulse sources (e.g. pile drivers and forging presses) or repetitive sources (e.g. pavement breakers), or sources which operate intermittently, but which would produce continuous vibration if operated continuously (for example, intermittent machinery, railway trains and traffic passing by). This type of vibration is assessed on the basis of vibration dose values in Table 2.4.
2.2 Application of the criteria
The criteria presented in Sections 2.3 and 2.4 should be applied when assessors are evaluating the effects of human exposure to vibration from industry, transportation and machinery. They are not intended to cover emissions from blasting, or vibration in vehicles or in special-purpose moving structures (e.g. amusement rides).
When applying the criteria, it is important to note that vibration may enter the body along different orthogonal axes, i.e. x-axis (back to chest), y-axis. (right side to left side) or z-axis (foot to head) (see Figure 2.1). The three axes are referenced to the human body. Thus, vibration measured in the horizontal plane should be compared with x- and y-axis criteria if the concern is for people in an upright position, or with the y- and z-axis criteria if the concern is for people in a lateral position (e.g. asleep at night). This is important in ensuring that the correct frequency weighting is applied to the relevant axis of vibration. Where the orientation of the occupant is unknown or could vary, then the most conservative approach should be adopted.
Figure 2.1 Orthogonal axes for assessment of human exposure to vibration (redrawn from BS 6472-1992)
The adverse effects of vibration on people almost invariably occur inside buildings or other structures. Satisfactory values for sources of vibration are therefore usually set for locations indoors. From a planning viewpoint (or for convenience of measurement), it may sometimes be necessary to translate indoor vibration values to values in the ground (for example, when a building has not yet been constructed or when access to an indoor location is not readily available).
Indoor vibration values caused by an external source can be measured externally (in the ground) and translated to indoor values or measured internally, and then compared to the criteria in Tables 2.2 and 2.4.
In situations where resonance of the building occurs, indoor values may be greater than the external ground vibration values produced by the same source (see Section 4.2 for more detail).
In this case, the operator should respond to complaints and assess the vibration values case by case. For a more detailed assessment, users of this guideline may choose to perform indoor measurements or refer to relevant texts and the literature in order to translate ground vibration values to indoor values. Sufficient justification should accompany whichever approach is used in an assessment.
Some people may perceive vibration at values below those given in Tables 2.2 and 2.4. In some cases it may be prudent to design to lower vibration values to further reduce the likelihood of complaint.
2.3 Acceptable values for continuous and impulsive vibration (1-80 Hz)
Acceptable values of human exposure to continuous and impulsive vibration are dependent on the time of day and the activity taking place in the occupied space (e.g. workshop, office, residence or a vibration-critical area). Guidance on preferred values for continuous and impulsive vibration acceleration is set out in Table 2.2.
Evidence from research suggests that there are summation effects for vibrations at different frequencies. Therefore, for the evaluation of vibration in relation to annoyance and comfort, overall weighted rms acceleration values of the vibration in each orthogonal axis are preferred (BS 6472).
The frequency weightings applied should be as follows, which are derived from the base curves for acceleration rms as shown in Figures B1.1 and B1.2:
- z-axis-weighting Wg for arms, defined in BS 6841-1987, as reproduced in Appendix B3
- x-, y-axes-weighting Wd for arms, defined in BS 6841-1987, as reproduced in Appendix B3.
There is a low probability of adverse comment or disturbance to building occupants at vibration values below the preferred values in Table 2.2. Activities should be designed to meet the preferred values where an area is not already exposed to vibration. Where all feasible and reasonable measures have been applied, values up to the maximum value may be used if they can be justified. For values beyond the maximum value, the operator should negotiate directly with the affected community.
Situations exist where vibration above the preferred values can be acceptable, particularly for temporary disturbances and infrequent events of short term duration. An example is a construction or excavation project. See Section 2.5 for more detail on short-term works.
Table 2.2 Preferred and maximum weighted rms values for continuous and impulsive vibration acceleration (m/s2)1-80 Hz
| ||Preferred values||Maximum values|
|Location||Assessment period1||z-axis||x- and y-axes||z-axis||x- and y-axes|
|Critical areas2||Day- or night-time||0.0050||0.0036||0.010||0.0072|
|Offices, schools, educational institutions and places of worship||Day- or night-time||0.020||0.014||0.040||0.028|
|Workshops||Day- or night-time||0.04||0.029||0.080||0.058|
|Critical areas2||Day- or night-time||0.0050||0.0036||0.010||0.0072|
|Offices, schools, educational institutions and places of worship||Day- or night-time||0.64||0.46||1.28||0.92|
|Workshops||Day- or night-time||0.64||0.46||1.28||0.92|
- Daytime is 7.00 am to 10.00 pm and night-time is 10.00 pm to 7.00 am
- Examples include hospital operating theatres and precision laboratories where sensitive operations are occurring. There may be cases where sensitive equipment or delicate tasks require more stringent criteria than the human comfort criteria specified above. Stipulation of such criteria is outside the scope of this policy, and other guidance documents (e.g. relevant standards) should be referred to. Source: BS 6472-1992
2.3.1 Example of continuous vibration applications
A continuous broadband vibration signal was measured in the z direction for 15 hours during the daytime at a residence. The rms acceleration values are shown in Table 2.3. Applying the weighting values for the z-axis (from BS 6841, reproduced in Appendix B3) in a 1/3-octave band spectrum from 1 to 80 Hz gives the result shown in Table 2.3.
Reference to Table 2.2 reveals that the weighted rms acceleration of 0.026 m/s2 is above the 0.01 m/s2 preferred vibration value for residences during the daytime.
Table 2.3 Sample rms acceleration values from continuous vibration application in the z direction for 15 hours during daytime. Weighting values for the z-axis are from BS 6841 in a 1/3-octave band spectrum, 1-80 Hz
|Frequency Hz||ms accel. m/s2 z-axis||Weighting z-axis||Weighted rms accel. m/s2 z-axis||Weighted rms accel. squared z-axis|
|Sum of the squares = ||0.000676|
|Weighted rms acceleration (square root of the sum) =||0.0260|
2.4 Acceptable values for intermittent vibration
When assessing intermittent vibration, use the vibration dose value (VDV). The VDV is given by the fourth root of the integral with respect to time of the fourth power of the acceleration after it has been weighted. This is the root-mean-quad approach. The use of the fourth power method makes VDV more sensitive to peaks in the acceleration waveform. VDV accumulates the vibration energy received over the daytime and night-time periods. The vibration dose is fully described in BS 6472-1992. Acceptable values of vibration dose are presented in Table 2.4.
Alternatively, vibration velocity can be used to broadly estimate VDVs; however, where possible acceleration should be used when determining VDV. The relevant formulae for use with velocity measurements are provided in Appendix B.
2.4.1 Calculating vibration dose value
Where vibration comprises repeated events, each of a similar value and duration, a VDV may be calculated. The following formula requires the overall weighted rms acceleration as determined in Section 2.3 over the frequency range 1 to 80 Hz:
Appendix A describes how to calculate the estimated VDV (eVDV) as a screening method. The VDV method should be used in preference to the eVDV method when the vibration dose is calculated.
Where there are repeated vibration events of variable magnitude, the total vibration dose for the relevant day or night period may be obtained by summing the N individual vibration doses for each group using the following formula:
where VDVi is the individual dose value.
2.4.2 Vibration dose values
Table 2.4 sets out acceptable VDVs for intermittent vibration.
There is a low probability of adverse comment or disturbance to building occupants at vibration values below the preferred values. Adverse comment or complaints may be expected if vibration values approach the maximum values. Activities should be designed to meet the preferred values where an area is not already exposed to vibration. Where all feasible and reasonable measures have been applied, values up to the maximum range may be used if they can be justified. For values beyond the maximum value, the operator should negotiate directly with the affected community.
Table 2.4 Acceptable vibration dose values for intermittent vibration (m/s1.75)
|Preferred value||Maximum value||Preferred value||Maximum value|
|Offices, schools, educational institutions and places of worship||0.40||0.80||0.40||0.80|
1 Daytime is 7.00 am to 10.00 pm and night-time is 10.00 pm to 7.00 am.
2 Examples include hospital operating theatres and precision laboratories where sensitive operations are occurring. These criteria are only indicative, and there may be a need to assess intermittent values against the continuous or impulsive criteria for critical areas.
Source: BS 6472-1992
2.5 Short-term works
When short-term works such as piling, demolition and construction give rise to impulsive vibrations, undue restriction on vibration values may significantly prolong these operations and result in greater annoyance. Short-term works are works that occur for a duration of approximately one week.
In circumstances where work is short term, feasible and reasonable mitigation measures have been applied, and the project has a demonstrated high level of social worth and broad community benefits, then higher vibration values (above the maximum) may apply. In such cases, best management practices should be used to reduce values as far as practicable, and a comprehensive community consultation program should be instituted. An example of a possible management strategy would be to restrict the times during which high vibration values occur to the least sensitive times of the day. Typical issues covered in a consultation program include a public contact point for handling complaints, and early notification of proposed operations and any significant change to operations.
2.5.1 Example of managing vibration impacts from construction
Necessity is the mother of invention-alternative work practices can be found when there is a pressing need to do so.
A construction company began piling works for a new apartment building in an inner city suburb. This building represented a late stage of the total redevelopment of their site and involved installing piles into a mud and sand layer, each pile being approximately 20 metres in depth. Approximately 85 piles needed to be installed across the site.
During this part of the construction phase the company undertook stability tests on the completed piles and found that the surrounding soil required compaction. Although this was an unforseen event, it could be easily remedied through standard compaction techniques.
The company then began to use a deep-level vibrocompaction unit around the piles. Vibration from this unit resulted in complaints to the local council from neighbouring residents concerned about potential structural damage to their buildings.
As the complaints were arriving, the company undertook further compaction tests and found that the upper 3 metres of the sand layer was not compacted to a stable level. To remedy this the company then began using a large, heavy steel plate dropped from a height to compact the upper sand layer around the piles after the deep level vibro-compactor had moved to the next pile.
The result of this strategy was to expose residents to a significant intermittent vibration level. Residents began to experience cosmetic damage to the interior of their apartments and demanded that council take action. Council gave the company a notice of intention for works to stop.
The company met with the most concerned residents of the neighbouring apartment buildings, which consisted of at least 750 units, in their individual apartments, to assess damage and monitor the noise and vibration that each resident experienced. The company also trialled dropping the steel plate from various levels to determine whether there was an acceptable height that would both achieve the level of compaction required and alleviate the residents' concern. The company settled on dropping the plate from three-quarters of the initial height.
At the same time, council undertook separate vibration testing and concluded that although the level of vibration produced from the threequarter drop would not result in structural damage to surrounding buildings, it would still cause annoyance to neighbours. Council served an order on the company, requiring it to cease all works onsite until it was able to provide a construction methodology that would satisfy council that residents would not be affected. This order effectively put an end to the continued use of dropping the steel plate.
Representatives of the company met with council and put forward a methodology that they were convinced would alleviate residents' concerns about annoyance from vibration. This involved the use of a 25-tonne roller, which council allowed on the proviso that the noise levels were within a specified range and that this method of compaction was used only on conclusion of the deep level vibration compaction method. Council accepted this methodology on the basis that as soon as a 'reasonable complaint' was received from an affected resident, then site works would have to cease and another methodology would have to be found.
The company also sent potentially affected residents a newsletter informing them of their alternative methodology for site compaction works, when its use would begin and expected operating timeframes. No further complaints were received about compaction vibration from this site.
Figure 2.1 Orthogonal axes for assessment of human exposure to vibration (redrawn from BS 6472-1992)
Page last updated: 12 June 2013